I don't know what may be breaking NDA to say, but I think it's been widely reported that some of Apple's own apps, including Preview, Final Cut Pro, and iMovie do not work. Quicken Essentials for the Mac and Microsoft Outlook 2011 for the Mac are broken. Logos is displaying some texts with missing words.

"Further, Apple agrees that You will not be bound by the foregoing confidentiality terms with regard to technical information about pre-release Apple Software and services disclosed by Apple at WWDC (Apple’s Worldwide Developers Conference), except that You may not post screen shots, write public reviews or redistribute any pre-release Apple Software or services."

I don't know what may be breaking NDA to say, but I think it's been widely reported that some of Apple's own apps, including Preview, Final Cut Pro, and iMovie do not work. Quicken Essentials for the Mac and Microsoft Outlook 2011 for the Mac are broken. Logos is displaying some texts with missing words.

I should add that folder icons sometimes do not display in the Finder.

Again, though, I've not had any problems with Accordance.

I hope that the next release of Yosemite (maybe this next week) will fix some of these initial issues. In my experience of running OS X betas, they usually become very solid early on. I ran the beta for Mavericks without issue for months before it was finally released.

I had the early iOS 8 betas in place on my iPhone and iPad but had to go back to iOS 7 because they definitely weren't ready. I may give them a few builds before I try them again.